The invention generally relates to power supply control systems, and relates in particular to adjustable control of voltage regulators.
Conventional controllers for voltage regulators, such as switched mode controller systems, include a controller interposed between a power source and a load, such as a digital signal processor. For example, as shown in FIG. 1, a conventional switched mode controller system includes an adjustable voltage regulator such as a switched mode converter 10 that couples a power supply 12 to a digital signal processor 14. The switched mode converter 10 receives a power supply input voltage 16 from the power supply 12 at a Vinps node and provides a pulse width modulated signal at output node sw. The pulse width modulated (pwm) signal is then low pass filtered by an inductor 20 and capacitor 24 to provide an output voltage 18 (Vout) to the digital signal processor 14.
The input voltage Vinps is typically provided to the converter 10 using a filter capacitor 22 that is also coupled to ground, and the output voltage is typically provided to the digital signal processor 14 using the filter capacitor 24 that is also coupled to ground. The controller 10 also includes a reference voltage 26 at a Vref node, and receives a feedback signal 28 at a feedback fb node.
The feedback signal is provided by a voltage divider circuit that includes a first resistor 30 (R1) that is coupled to the output signal 18, and a second resistor 32 (R2) that is coupled to ground. The voltage reference signal may be either provided via an external connection as shown or may be provided internally. The feedback signal 28 and the voltage reference signal are provided to a differential amplifier 13, and the output of the differential amplifier is provided to a pwm generation unit 11.
The pwm signal at the node sw is provided by the pwm generation unit 11 responsive to the output of the differential amplifier is employed to control the output of the supply input voltage Vinps as well as the output of the differential amplifier.
The voltage Vout is provided by the relationship Vout=Vref(1+R1/R2). The voltage Vout is typically adjusted by changing the values of the resistors R1 and R2. The voltage Vout however, may not be made to be less than Vref and such adjustments must be made by physically changing resistors or adjusting potentiometers. Certain further switched mode controllers employ a digital potentiometer that may be adjusted by changing a digital wiper value on the digital potentiometer using a digital control interface. Although the use of such a digital potentiometer may permit the controller to switch a power supply voltage in real time, the control circuit requires additional complex digital circuitry.
There is a need, therefore, for a more efficient and economical adjustable voltage controller system. There is further a need for an adjustable voltge controller that may be adjusted in real time and may be fully adjusted such that Vout may be adjusted to be less than Vref.